[AMRadio] Drying out HV transformers / Chokes

doxemf at aol.com doxemf at aol.com
Sun Sep 18 13:00:11 EDT 2005

Hello Larry and All,
I have several 2.5v and 10v rusty,dirty, and rattling UTC small can S series filament transformers that I want rebuild and would like to know a source for transformer varnish and potting material, wax,tar, or whatever.
On pulling the cover off the most rattling around one I found only sections of corrugated cardboard to be the "packing/potting"  material !!. I would like to use something better and improve the heat transfer as these seem to be really small construction for the rated current. I intend to use the 10v units for 813/814/805 family.
Any suggestions would be appreciated.
Bill KB3DKS/1
-----Original Message-----
From: Larry Will <lhwill at verizon.net>
To: w8hrq at lemleys.org; Discussion of AM Radio <amradio at mailman.qth.net>
Sent: Sun, 18 Sep 2005 10:41:41 -0400
Subject: Re: [AMRadio] Drying out HV transformers / Chokes

Here is the section in my article from ER Magazine on rebuilding an RCA BTA-1R1 on the homemade over I used with great sucess. all you need is a thermostatically controlled hotplate a thermometer and a hood. 
.from my RCA BTA-1R! article in ER. 
A check of all the iron with a 1000V 1000 megohm ohmmeter showed excessive leakage (less than 1000 megs) in the modulation reactor, the driver plate transformer, and the control transformer. The control transformer makes 110VAC for relays and lamps from the 240V input. The smaller transformers were baked in the kitchen oven at 140 degrees F for 5 hours. For the very heavy 50 henry modulation reactor, I fashioned a homemade "oven" using a thermostatically controlled single burner hotplate and a hood made from an old water heater jacket (Figure 1). This allowed me to cook the transformer out in the garage near the rig. An oven thermometer allowed me to set the oven temperature to 140 degrees F and after 25 hours of "baking", the leakage was cured. All of these transformers and chokes were then dipped in transformer varnish to re-seal the winding from new moisture incursion. 
Larry W3LW 

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